Circular end shield for mixer rotors



April 8, 1952 s. BOLLING CIRCULAR END SHIELD FOR MIXER ROTORS Filed Dec. 4, 1950 INVENTOR 1 BY I ATTORNEYS.

Patented Apr. 8, 1952 CIRCULAR END SHIELD FOR MIXER ROTORS Stewart Bolling, Cleveland, Ohio Application December 4, 1950, Serial No. 199,014

'1 Claim. (01. 259-137) This invention relates to the construction of heavy duty intensive or internal mixers used in the mixing of dry powders, pigments, staples or other materials to be incorporated or dispersed in a base binder such as rubber, asphalt, plastics, or the like.

To my knowledge, in all mixers such as the Banbury mixer heretofore produced, the practice has been to cast or forge the end of the rotor or mixing element to conform to the shape of the flute when seen in cross section at said end. This shape will always be an irregular one.

In mixers of this type, the rotor works within a stationary casing, with the rotor ends of irregular cross section being respectively disposed against the opposite casing walls. In this connection, it is essential in such a structure that some clearance be provided between the rotor ends and the stationary casing walls since there must always be clearance between a rotating end face of one member and the face of a stationary member in which the first member rotates. Further, since rotors in mixing apparatus of the type described must operate at widely varying temperatures, from cold to very hot, added clearance must be provided for to allow for endwise expansion of the rotors, and then to these clearances must be added the inherent clearance and wear of thrust devices which hold the rotors in endwise position in the casing. Thus, where a rotor is, for example, 36 inches in length, the running clearance from rotor end to casing is considerable and at least three sixty-fourths of an inch must be provided before the machine is ever placed in use, for running clearance and expansion. This clearance shortly increases to a material extent with wear.

Considering how this wear occurs, it has been observed as the irregular rotor end drags the end casing, some of the dry powder or other material to be mixed is caught in the clearance and dragged around with the rotor end. This begins causing wear and as wear increases, by-passing begins and increases during the continued use of the apparatus and is hastened by deposit in the machine, for mixing, of various abrasive powders.

The main object of the present invention is to eliminate or reduce materially the deficiencies above-noted by improving in a novel manner never previously suggested in the art, the construction of the rotor ends.

More specifically, it is an important purpose of the present invention to transfer the objectionable axial clearance between rotor end and casing to a peripheral or radial clearance that can be much closer, will not be affected by endwise expansion or by clearance of thrust devices; and by means of which wear can be readily controlled.

With the foregoing and other objects in view which will appear as the description proceeds, the invention consists of certain novel details of construction and combinations of parts, hereinafter more fully described and pointed out in the claim, it being understood that changes may be made in the construction and arrangement of parts without departing from the spirit of the invention as claimed.

Referring to the drawings Fig. l is a vertical section through stationary casing walls of a mixer in whichare journaled the opposite end portions of rotors having their ends formed in accordance with the presentinvention, portions being broken away.

Fig. 2 is a transverse section taken substantially on line 2-2 of Fig. 1.

Referring to the drawings in detail, opposed stationary casing walls I have formed in their inner surfaces annular recesses 2 in which are mounted correspondingly formed wear plates 3. These surround the bearing openings 4 of said casing Walls, said bearing openings in the present instance being enlarged at their outer ends as at 5 and receiving rings 6 correspondingly enlarged at 1. Journaled in these bearing openings are the spindles 8 formed at opposite ends of a rotor or mixing element including the core 9 formed with the spirally disposed flutes Hi.

The cross sectional or end configuration of the flute I0 is seen in Fig. 2 and as will be seen the formation of the flute upon the otherwise circular core defines a lateral projection extending irregularly of the core body at one side thereof.

Heretofore, it has been the practice merely to provide an end shroud at the flute end, the outer configuration of this shroud being irregular and in substantial correspondence with the irregular shape of the fiute end. This irregular flute end, when placed in use, has been spaced from the inner surface of the casing wall i to allow for the various clearances hereinbefore noted, and in dragging over said face, has caused the material being mixed to enter the clearance and produce wear.

In accordance with the present invention I cast or forge on the rotor ends circular end shields I I which are thereafter machined to true circular shapes. As seen from Fig. 2, these circular end shields are concentric with the core 9, that is, with the axis of rotation of the rotor, and as will be further noted from Fig. 2, the wide outer edge of the flute I is flush with or in coincidence with the periphery of said shield I l.

The inner face of the end shield ll, additionally, is formed with a continuous circumferential depression I2 curved transversely thereof as seen from Fig. 1. This construction tends to assist the flutes I0 in turning the mass of material being mixed and plowing it back toward the middle of the mixing chamber. Parenthetically, it may be noted that most usually, the rotors of mixers oi the type stated plow from end to middle of the working chamber.

By reason of the construction described above, I am able to reduce to a minimum the clearance between the outer surface of each end shield-and the inner surface of the stationary casing wall I. Further, the possibility of dry material entering into the clearance space, even after said space is reduced to a minimum, is eliminated, since the circular end shield construction allows the use of shroud plates l3 formed with openings l4 and mounted upon the inner surfaces of the stationary casing walls I the end shields ll bearing in said openings. These shroud plates can be simple and inexpensive and when worn are readily replaceable at low expense, with the replacement plates being easily bored with openings H of a proper diameter to take up wear in the periphery of the end shield H.

or additional importance is the fact that the end shield, having radial rather than axial clearance, does not in itself act like a reciprocating pump to compress and discharge material being mixed into the space between the spindle of the rotor and the bearing openings of the end frames (bearing in mind here that the direction of thrust reverses in every revolution of the rotor flutes). Inj mixing apparatus as heretofore constructed, the rotor moves back and forth and the open end areas become, in point of actual fact, not unlike pump cylinders. In the present invention, this endwise pumping is eliminated by the end shields which hold the rotor centrally positioned between the end frames or stationary casing walls I.

What is claimed is:

In a batch mixer of the type comprising a casing having an elongated substantially circular mixing chamber, parallel end walls closing opposite ends of the chamber, said end walls having bearing openings extending therethrough and opening into the chamber in axial alignment with the longitudinal axis thereof, an elongated rotor mounted in said casing for rotation about the longitudinal axis thereof, trunnions carried by opposite ends of the rotor and, mounted for rotation in the bearing openings and a spiral rib carried by the rotor and projecting outwardly therefrom, means to prevent contact of the contents of the chamber with the trunnions and the walls of the bearing openings comprising outflanges, said shroud plates being of a thickness substantially equal to the thickness of the flanges and encircling the flanges in closely spaced relation thereto.

STEWART BOLLING.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,406,666 Lohmann Feb. 14, 1922 1,990,555 Loomis Feb. 12, 1935 2,264,237 Broan Nov. 25, 1941 

